Use a spiralizer to cut the zucchini into thick noodles.
Heat a skillet over high heat. Add the whole tomatoes and cook 4-5 minutes, or until the skin begins to blacken and blister. Immediately remove from heat and let cool. Return the pan to the burner and add the zucchini noodles. Cook 2-3 minutes, or until just softened. Add the corn and cook until heated through.
Transfer the zucchini and corn to a large mixing bowl. Chop the tomatoes and add them to the bowl.
In a food processor, process the cilantro, oil, and vinegar, until smooth. Season with salt and pepper; pour over the vegetables. Toss to coat.
Meanwhile, spray a nonstick skillet with cooking spray and set it over medium-high heat. Season the chicken breasts on both sides with salt, pepper, and chili powder. Add the chicken to the hot pan and cook until golden brown on one side, about 5 minutes. Turn the chicken and cook it another 5-7 minutes, or until it's just cooked through. Reduce the heat to medium-low and cover each pie of chicken with two cheese slices. Cover and cook 5 minutes to melt the cheese.
Serve the smothered chicken over the zucchini noodles.